Phase and frequency-locked loop circuits

ABSTRACT

The invention relates to phase and frequency-locked loop circuits (PLL and FLL circuits) with a controllable tracking oscillator whose signal phase relationship or frequency, respectively, is influenced by an external parameter, a reference oscillator, as well as a phase or frequency comparator, the output signal of which is used to control the tracking oscillator in such a way that any phase or frequency errors are reduced. The invention provides for an element for the measurement of the external parameter (such as a microprocessor) which is capable of receiving a signal representing the output signal of the phase or frequency comparator, and convert it into a measurement value that represents the present value of the external parameter. This external parameter can, for example, represent the ambient temperature or the supply voltage of the tracking oscillator.

FIELD OF THE INVENTION

[0001] The invention relates to phase and frequency-locked loop circuits(PLL and FLL circuits).

BACKGROUND OF THE INVENTION

[0002] PLL and FLL circuits are at present finding a plurality ofapplications in electronic circuits for the purpose of synchronizing afrequency-controllable tracking oscillator (usually a voltage-controlledoscillator [VCO]) in either phase or frequency with the signal of areference oscillator (such as a crystal-controlled oscillator), whosephase or frequency, respectively, is virtually constant in comparisonwith the voltage-controlled oscillator. The clock frequency generated bythe tracking oscillator is thereby greater by a certain factor (such as100) than the frequency of the reference oscillator, and is applied, viaa frequency divider, to a phase or frequency comparator, respectively,which generates the signal for the control of the tracking oscillator.The output signal generated by the tracking oscillator can then, forexample, be used as the system clock signal for a microprocessor.

[0003] Apart from the PLL and/or FLL circuits, nowadays a plurality offurther circuit components, to fulfill a variety of functions, aregenerally also integrated on the same chip. These may, for example,include circuit components for the measurement of certain parameters,such as the ambient temperature or a changing supply voltage, and whichmake this information available to other circuit components for whosefunctioning this information is of significance.

[0004] The micro-electronics industry is constantly striving to make thebest possible use of the space that is available on a microchip for thesum of the plurality of circuit components, and to reduce the size ofthese circuit components to the greatest possible extent. Thisrequirement has not been met in the best possible way in previouscircuits containing both a PLL or an FLL circuit, as well as circuitsfor the measurement of temperature and/or voltage, respectively.

SUMMARY OF THE INVENTION

[0005] The purpose of the present invention therefore is to provide aPLL or FLL circuit, respectively, in conjunction with a circuit for themeasurement of specific parameters (such as temperature or supplyvoltage), that will use less circuit space than previous embodimentsolutions, and that can also be produced more cost effectively.

[0006] This requirement is met by a phase-locked loop circuit (PLLcircuit) in conjunction with a controllable tracking oscillator whosesignal phase relationship is influenced by an external parameter, areference oscillator whose signal phase relationship is constant, aswell as a phase comparator to compare the phase relationship of thesignal supplied by the tracking oscillator with the phase relationshipof the signal supplied by the reference oscillator, and which suppliesan output signal characteristic of the phase shift to the trackingoscillator, with which this will be controlled in such a way that phaseerrors are reduced, and where furthermore an element for the monitoringof the external parameter is provided which is conceived in such a waythat it can receive a signal representing the output signalcharacteristic of the phase shift, and so change it into a measuredvalue which represents the real value of the external parameter.

[0007] Furthermore, this requirement is also met by the use of afrequency-locked loop circuit (FLL circuit) in conjunction with acontrollable tracking oscillator whose frequency is influenced by anexternal parameter, a reference oscillator whose frequency is constant,as well as a frequency comparator which compares the frequency of thesignal supplied by the tracking oscillator with the frequency of thesignal supplied by the reference oscillator, and which supplies anoutput signal characteristic of the frequency difference to the trackingoscillator, with which this will be controlled in such a way thatfrequency errors are reduced, and where furthermore an element for themonitoring of the external parameter is provided which is conceived insuch a way that it can receive a signal representing the output signalcharacterizing the frequency shift, and so change it into a measuredvalue which represents the real value of the external parameter.

[0008] The invention makes use of the fact that the level of the signaloutput by the phase/frequency comparator during the operation of a PLLor FLL control circuit, when the frequency of the tracking synchronizeris influenced by only one external parameter, such as the ambienttemperature, characterizes this parameter, so that the measured value ofthe parameter, such as the ambient temperature, can be determined fromthis with the help of one further element. The invention thereforeintegrates the previously used circuit components for the parameterdetermination into the PLL or FLL circuit itself and thereby bothreduces production costs as well as the requirement for circuit space ascompared with conventional solutions.

[0009] The element used to measure the external parameter therebypreferably includes a microprocessor. If the tracking oscillator is usedto supply the clock pulses for the microprocessor, there will be no needfor any further circuit components to achieve phase or frequencytracking, as well as the determination of parameters, as compared withexisting conventional methods. Advantageous further developments of theinvention are designated in the subclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The invention shall now by explained in exemplified form withreference to the drawing, where

[0011]FIG. 1 illustrates a PLL circuit, with a microprocessor for thedetermination of a temperature.

DETAILED DESCRIPTION OF THE DRAWINGS

[0012] The left-hand section of FIG. 1 here represents a conventionalPLL circuit 1. This conventional PLL circuit 1 comprises a referenceoscillator 2 which, in the present case, includes a crystal-controlledoscillator, and a controlled tracking oscillator 3 which, in the presentcase, is a digitally controlled oscillator (DCO).

[0013] The frequency fMCLK of the tracking oscillator 3 is greater by afactor N than the frequency fACLK of the reference oscillator 2. Thiswill be adapted to the frequency of the reference oscillator 2 by meansof a frequency divider 4 which is connected to the output of thetracking oscillator 3.

[0014] Provided is furthermore a phase comparator 6, whose first inputis connected to the output of the reference oscillator and whose secondinput is connected to the output of the frequency divider, and whichcompares the phase of the signal from the reference oscillator with thephase of the signal from the frequency divider 4, and which outputs anoutput signal 7 that is characteristic of the phase shift between thetwo signals.

[0015] By means of a digital filter 8, connected to the output of thephase comparator 6, this output signal 7 is converted into acorresponding digital signal 9, for the purpose of controlling thecontrollable tracking oscillator 3 in such a way that the phase shiftbecomes zero, and whereby at the same time the condition fMCLK=N*fACLKis satisfied, that is the frequency of the tracking oscillator 3 thencorresponds to the Nth multiple of the (constant) frequency of thereference oscillator 2.

[0016] Let it be assumed that the tracking oscillator 3 is embodied insuch a way that changes of the frequency fMCLK that are not caused bythe control signal 9 are essentially the result of influences by anexternal parameter. In the present example, this external parameter isassumed to be the ambient temperature T.

[0017] If the ambient temperature changes, this will cause a change ofthe frequency fMCLK of the tracking oscillator 3. This, in turn, causesa corresponding change in the level of the output signal 7 from thephase comparator 6, and therefore also of the output signal 9 of thedigital filter 8, including the output signal in digital form. At thesame rate as the temperature changes during the operation of the PLLcircuit, there will be a corresponding change of the output signal fromthe phase comparator 6 or of the output signal 9 from the digital filter9, characterizing this output signal in digital form, respectively.

[0018] This digital output signal 9 is now also applied to the signalinput 11 of a microprocessor 10, which is embodied in such a way that itcan determine the temperature from the signal characterized by the phaseshift and, therefore, the temperature change.

[0019] The microprocessor 10 may, for example, keep a lookup table inits memory which stores the assignment of the digital values output bythe digital filter with respect to the corresponding temperature values.With the help of this assignment system it becomes possible to determineon a continuous basis the actual present temperature value by comparingthe digital values of the control signal 9, supplied to the signal input11 of the microprocessor, with the values stored in the table.

[0020] In its preferred version, the microprocessor 10 has furthermore aclock input 12 at which the output signal of frequency fACLK, assupplied by the reference oscillator 2, is present. This is ofadvantage, since the temporal sequencing of the sampling of thetemperature measurement values can be adapted to the corresponding phasecomparator 6 and its time schedule at the delivery of the control signal9. This means that a renewed sampling process of the temperaturemeasurement value, for example, is only significantly indicated when achange of the digital control signal has just taken place. If the changeof the digital control signal 9 is controlled by the signal of frequencyfACLK, supplied by the reference oscillator 2, the temporal sequence ofthe sampling process of the temperature values is preferentially alsocontrolled by means of this signal. This means that whenever, forexample, the phase comparator 6 outputs a control signal 9 at thepositive slope of the reference oscillator signal, a new sampling valuefor the determination of the temperature can be supplied to themicroprocessor for evaluation.

[0021] In another embodiment of the invention, the clock signal of thereference oscillator can also be used as the microprocessor clock, sothat there will be no need for the microprocessor 10 to have its ownclock signal generator.

[0022] The precise determination of the temperature value can be bymeans of various different numerical methods, known in the context ofmathematical statistics.

[0023] It is, for example, possible to store and accumulate a specificnumber of sampling values in succession at specified temporal intervalsin the memory of the microprocessor 10, in order to compute a mean valueof the temperature and, therefore, increase the precision of themeasurement.

[0024] A sliding average value can also be obtained by replacing thelatest value of the number of sampling values by the most recentsampling value.

[0025] The tracking synchronization circuit according to the inventionis, of course, not limited to applications in PLL circuits, but canequally well be used with frequency tracking synchronization circuits,where a frequency comparator is provided instead of the phase comparatorshown in FIG. 1.

[0026] It is, of course, not necessary either that the trackingoscillator should be embodied as a digitally controlled oscillator, buta conventional voltage controlled oscillator (VCO) can be used equallywell.

[0027] The external parameter, from which the frequency (or phase,respectively) of the tracking oscillator depends, must not of necessitybe represented by the ambient temperature either. It can, for example,also be the supply voltage for the tracking oscillator that essentiallyinfluences the frequency or the phase of the tracking oscillator. Insuch a case, the microprocessor represented in FIG. 1 would then supplya measurement value for the supply voltage of the tracking oscillator.

[0028] Even a digital filter does not, of course, constitute a necessaryprecondition. Conceivable is equally well an embodiment where ananalogue signal, supplied by a low-pass filter, is digitized by ananalogue-to-digital converter within the microprocessor.

[0029] It is, of course, also not necessary that the element for themeasurement of the external parameter should consist of amicroprocessor, but a logic circuit capable of generating a measurementvalue of the parameter from the control signal 9 would be equallysuitable.

1. A phase locked loop (PLL) circuit comprising: a controllable tracking oscillator having a signal phase relationship dependent on an external parameter; reference oscillator having a constant phase relationship; a phase comparator to compare the phase relationship of the signal supplied from said controllable tracking oscillator with the phase relationship of the signal supplied by the reference oscillator and outputs an output signal corresponding to the phase shift to the tracking oscillator to reduce phase error; an circuit for monitoring the external parameter to receive a signal to represent a characteristic of the output signal of the phase shift; and convert a signal to a measured valued which represents the real value of the external parameter.
 2. A phase locked loop (PLL) circuit comprising: a controllable tracking oscillator having a frequency dependent on an external parameter; reference oscillator having a constant frequency; a frequency comparator to compare the frequency of the signal supplied from said controllable tracking oscillator with the frequency of the signal supplied by the reference oscillator and outputs an output signal corresponding to the frequency different to the tracking oscillator to reduce phase error; an circuit for monitoring the external parameter to receive a signal to represent a characteristic of the output signal of the phase shift; and convert a signal to a measured valued which represents the real value of the external parameter.
 3. A phase lock loop circuit according to claim 1, where the external parameter is represented by the ambient temperature.
 4. A phase lock loop circuit according to claim 1, where the external parameter is represented by the supply voltage of the tracking oscillator.
 5. A phase lock loop circuit according to claim 1, where the circuit for the measurement of the external parameter includes a microprocessor having a signal input capable of receiving the signal representing the output signal characteristic of the frequency shift.
 6. A phase lock loop circuit according to claim 4, where an analogue-to-digital converter is provided, which is connected between the output of the phase or frequency comparator, respectively, and the signal input of the microprocessor.
 7. A phase lock loop circuit according to claim 5, where the tracking oscillator is a digitally controlled oscillator which receives the digital signal generated by the analogue-to-digital converter.
 8. A phase lock loop circuit according claim 2, wherein the frequency of the reference oscillator is lower than the fundamental frequency of the tracking oscillator, and where a frequency divider is provided between the output of the tracking oscillator and the input of the phase or frequency comparator, respectively.
 9. A phase lock loop circuit according to claim 2, where the external parameter is represented by the ambient temperature.
 10. A phase lock loop circuit according to claim 2, where the external parameter is represented by the supply voltage of the tracking oscillator.
 11. A phase lock loop circuit according to claim 2, where the circuit for the measurement of the external parameter includes a microprocessor having a signal input capable of receiving the signal representing the output signal characteristic of the frequency shift.
 12. A phase lock loop circuit according to claim 4, where an analogue-to-digital converter is provided, which is connected between the output of the phase or frequency comparator, respectively, and the signal input of the microprocessor.
 13. A phase lock loop circuit according to claim 5, where the tracking oscillator is a digitally controlled oscillator which receives the digital signal generated by the analogue-to-digital converter. 